Powdered milk questions

March 5, 2017 8:09 AM

What's the actual food science reasoning behind these directions on a packet of powdered milk?

As a bit of background, it totally irks me when a food product recommends something without saying why. In this case, the powdered milk specifically suggests that when reconstituting with water, to:

A) use a glass container
B) that is air tight
and C) allow it to sit in the refrigerator overnight

Okay, (C) makes sense I guess because it gives it time to fully dissolve or something. But really? Does it really need 8+ hours to do that? Wouldn't the initial temperature of the water and the amount of stirring make a hell of a lot more of a difference? Is there something about the milk protein that actually needs this time?

(A) makes no sense whatsoever. Regular milk comes in plastic jugs. Making a plastic container that does not contaminate the fluid it holds is a solved problem. Why do I need glass for this?

I suppose (B) is common sense, in that you wouldn't put an open glass of milk in the fridge as some of the water content would evaporate (?). But is it actually necessary to be air tight? (I know none of this is strictly necessary; I want to know if it makes a difference in terms of taste, which is what the label is claiming.) I've got some pitchers that are covered but which aren't air-tight. Is that honestly going to make a difference? Why would they say this if it was irrelevant?!

Bonus question

The packet talks up the fact that powdered is cheaper than real milk, and I seem to recall hearing about people on extreme budgets using powdered milk to save money. It makes sense since there's so much shipping weight savings. But that's totally not the case. At my local grocery store, a thing that makes 3 quarts costs about $4, and at Amazon, a thing that makes 8 quarts costs $9 (the lowest price per weight I could find, so definitely not the gourmet stuff.) In both cases, that's more than a dollar per quart, whereas a gallon of milk is like, what $3.50? The hell? I also checked ebay to see if I could buy a prepper-style tub of the stuff for ultra cheap, but it came out about the same as the Amazon price.

posted by Rhomboid to Food & Drink (21 answers total)

Fresh milk is a common loss leader.
posted by aniola at 8:15 AM on March 5, 2017

Pricing out quart packets of milk compared to a gallon of milk is comparing apples to oranges. Compare quart packets of milk to quarts of milk. The price per gallon of milk when you're only buying one quart at a time is MUCH higher than $3.50. If you're the sort of person who only drinks a quart of milk a week, which a lot of folks do, a gallon is going to expire before you can drink all of it, and that's money wasted. If your milk needs are low and inconsistent, and or if you don't have consistent access to electricity to keep milk cold, that's how powdered milk can be a cost savings.
posted by phunniemee at 8:16 AM on March 5, 2017 [7 favorites]

As someone who grew up drinking milk reconstituted from powder, I can say that there is a definite difference between milk that has been freshly mixed from powder (we used a blender to do it, so no lack of stirring there) and the same milk that has sat in the fridge overnight; there is a certain off-taste to the former that I can only describe as "powdery" that goes away after sitting for some hours. I have no idea why, though.

We also used airtight glass containers (mason jars), so I can't comment on why the other two recommendations are made.
posted by Johnny Assay at 8:26 AM on March 5, 2017 [2 favorites]

I dont usually need to have milk in the house so sometimes I buy a single serving if I need it for a recipe. It's at least a dollar for 8 oz.
posted by Room 641-A at 8:28 AM on March 5, 2017

A and B are about mitigating contamination risk. Plastic is much softer than glass and scratches easily. Scratches, even tiny ones you can't see provide bacteria with places to hang on through washing. So A is about making sure there aren't any dormant bugs in the container before you introduce milk, which is great food for bacteria as well as mammals. And B is about keeping bugs out once you've put it in there. The factories where milk is packaged have processes beyond whats available to the typical consumer to make sure their plastic milk jugs are sterile before filling them.
posted by rodlymight at 8:34 AM on March 5, 2017 [14 favorites]

I'm just guessing, but: glass can be sterilized at home, plastic can't (you can't boil household plastics). Also, glass gets colder faster and stays cold longer. An air-tight seal prevents an off taste from developing.

I have a suspicion that the manufacturer is worried that people will think that powdered milk is safe to keep unrefrigerated because it arrives unrefrigerated, or that they'll use an old plastic milk jug that isn't properly sterile, or something.
posted by blnkfrnk at 8:35 AM on March 5, 2017 [4 favorites]

I glanced at Harold McGee's On Food and Cooking and found a clue as to why recommendation (B) (and possibly (A)) is made:

Most powdered milk is made from low-fat milk because milk fat quickly goes rancid when exposed to concentrated milk salts and atmospheric oxygen, and because it tends to coat the particles of protein and makes subsequent remixing with water difficult.

So (B) may have something to do with avoiding rancidity, and (A) may have something to do with making sure the protein particles are fully dissolved. (Note that even skim milk has a small amount of residual fat; the USDA requires it to be less than 0.5 grams per serving, but not zero).
posted by Johnny Assay at 8:40 AM on March 5, 2017

Response by poster: Oh hey, great answers so far, but you just reminded me of something I meant to ask but forgot. Why is milk in powder form completely stable for years, requiring no refrigeration, but as soon as you mix it with water, watch out, we've got a ticking time bomb here (even if kept cold)?
posted by Rhomboid at 8:44 AM on March 5, 2017

If your milk needs are low and inconsistent, and or if you don't have consistent access to electricity to keep milk cold, that's how powdered milk can be a cost savings.

I am a person who only keeps milk on hand to add to black tea on weekdays (2 teaspoons per day) and for masala chai on weekends (200 ml/7 fl oz per day). At most, my max weekly consumption of milk is about 450 ml/roughly 1/2 quart, and much less if I don't make masala chai on weekends.

Given that I often don't make tea every day, have weekend brunch plans, etc., it's much more cost-effective for me to buy a jar of milk powder (which I usually get at the Indian store, since they seem to stock lots and lots of milk powder) that will last for weeks at a time.
posted by andrewesque at 8:47 AM on March 5, 2017

Why is milk in powder form completely stable for years...[but it goes bad quick when water is added]?

Because harmful bacteria need water to survive and proliferate. Dehydration is a common and ancient way to preserve food.. Fresh beef goes bad fast, jerky lasts for decades. Same for dried fish, raisins... and also powdered milk.
posted by SaltySalticid at 8:48 AM on March 5, 2017 [13 favorites]

but as soon as you mix it with water, watch out, we've got a ticking time bomb here (even if kept cold)?

Yup. Water is life, Usul.
posted by zamboni at 8:51 AM on March 5, 2017 [6 favorites]

Also, more on glass. Yes, it can be sterilized at home, and yes, it is harder/smoother, which provides less places for things to get stuck and possibly harbor bacteria. But there is an effect of the container surface on mixing too. If you doubt it, try to mix up some powdered milk in glass vs. plastic (or flour and water, or psyllium husk, or cocoa powder, etc.). I think you'll find that glass is functionally less sticky, and it is generally easier to mix powders into liquids in glass containers, compared to plastic. (PS I bet you must be irked a lot. I can hardly think of any packaged food instructions that explain the motivation or "why" any steps should be taken. MeFi mail me interesting examples that do! )
posted by SaltySalticid at 8:58 AM on March 5, 2017 [4 favorites]

On pricing: when checking food prices, never trust Amazon, or assume they are representative of anything sane or normal. I've seen $9 boxes of regular General Mills cereal there.

At my local grocery, powdered milk sells in boxes that make 8 qt, with a serving cost of $0.03 per oz. That is the same cost as their 1/2 gallon fresh jugs. Bigger boxes yet will get you below the per oz price of buying milk by the gallon. Also, keep in mind that fresh milk is more expensive in rural areas and remote places, and powdered milk becomes even more advantageous in that context.

(Moral of the story: poor people usually are not wrong when they do a thing to save money, and do not trust ebay or Amazon for real-world food prices.)
posted by SaltySalticid at 9:10 AM on March 5, 2017 [4 favorites]

Response by poster: It's great that your local grocery offers that item at that size and price, but mine doesn't. Amazon was cheaper than what I could get at the store.
posted by Rhomboid at 9:37 AM on March 5, 2017

(C) makes sense I guess because it gives it time to fully dissolve or something. But really? Does it really need 8+ hours to do that? Wouldn't the initial temperature of the water and the amount of stirring make a hell of a lot more of a difference? Is there something about the milk protein that actually needs this time?

I don't have access to the full version of this article, but its abstract suggests that rehydration characteristics of dried milk are an active area of research. So a more in-depth review of the literature than I can do with my access rights might get you the full information you want on this subject.
posted by Tandem Affinity at 11:09 AM on March 5, 2017

Try making it how you wish. How did it taste?
posted by humboldt32 at 11:50 AM on March 5, 2017 [3 favorites]

Those read to me as directions meant to optimize the taste of the product. Everything I've read about powdered milk says it's tastier after it's spent some time mixed and in the fridge, and the sealed glass container sounds like they're trying to get the customers to avoid having their milk pick up off flavours from plastics that've picked up flavours, or stuff in the fridge. It's pretty much exactly how I would prepare powdered milk if I was going to use it for drinking.

Maybe they're just fussing at their customers in hopes that they'll be fussy about reconstituting it, with the hope that purchasers will think it's a better-tasting product than the competitors'?
posted by kmennie at 12:21 PM on March 5, 2017 [1 favorite]

Adding on to the many reasons above, I wonder whether the instructions are a legal hedging, meant to cover the company's ass when someone mixes it wrong and gets sick. Sort of like the "Warning: Contents are hot" messages on coffee cups.
posted by ejs at 12:32 PM on March 5, 2017 [1 favorite]

The price vs. circumstances calculation changes if you're a long drive away from the store, or you only get food money once at the beginning of the month. Then you can't depend on getting some milk when you want it, so mixing it up to order makes a lot of sense.

Anecdata: In terms of price, when I was a kid, powdered milk was much cheaper (half to two-thirds the price) than fresh milk in the same quantity. I bought some for a recipe recently, and was shocked to see that the price is about even in my urban grocery stores (both a hipster-oriented store in Brooklyn, and a non-fancy neighborhood store in Flushing.) I had been considering going to powdered for everything to save money (I don't drink milk, I only cook with it or put some in coffee) but I figure that's not a workable strategy any more. (Concentrated frozen orange juice is still a pretty good deal, though.)
posted by blnkfrnk at 1:03 PM on March 5, 2017

Former poor person here. When I was a kid, powdered milk was definitely cheaper than the fresh kind, and even now I'm going to suggest that perhaps your local grocery's price on powdered milk is an outlier, because I'm pretty positive that I can buy a box at my local grocery that will make several gallons for about $6. Around here a gallon of milk is about $4.

Also when I was a kid, we would sometimes get food from the USDA, which included things like the infamous "government cheese", weird canned meat, and giant boxes of dry milk powder.

We never mixed it in a glass container. I'm pretty sure we just put it in a pitcher that you would make orange juice or kool-aid in. Nobody died or anything, so this might be one of those food safety directions that's there so you can't sue the manufacturer in case something goes wrong, but which has a vanishingly small chance of doing any harm.
posted by katyggls at 1:12 AM on March 6, 2017

Rhomboid: "Making a plastic container that does not contaminate the fluid it holds is a solved problem. Why do I need glass for this?"

Probably the other way around; they don't want users using milk jugs (which get contaminated with milk proteins) which would seem to be an obvious choice to mix/store reconstituted milk powder.
posted by Mitheral at 11:43 AM on March 6, 2017